Fix escaped backslash crash (#1870)

* Fix escaped backslash crash

Fixes #1855.

* Code review

Author: jathak

CHANGELOG.md

@@ -14,6 +14,8 @@
 * Produce a better error message for a nested property whose name starts with
   `--`.
 
+* Fix a crash when a selector ends in an escaped backslash.
+
 ## 1.57.1
 
 * No user-visible changes.

lib/src/utils.dart

@@ -114,7 +114,7 @@ int? _lastNonWhitespace(String string, {bool excludeEscape = false}) {
     if (!isWhitespace(codeUnit)) {
       if (excludeEscape &&
           i != 0 &&
-          i != string.length &&
+          i != string.length - 1 &&
           codeUnit == $backslash) {
         return i + 1;
       } else {